Curable resin composition, optical component and optical waveguide

ABSTRACT

The present invention is to provide a curable resin composition that is desirably used for manufacturing an optical part, in particular, an optical waveguide, that is superior in heat-resistant properties such as a heat-resistant decomposing property and a coloring-resistant property, and has its refractive index precisely controlled. 
     The present invention provides a curable resin composition, comprising:
         (A) a monomer that contains a polycyclic alicyclic hydrocarbon skeleton and two or more terminal radical polymerizable groups,   (B) a monomer that contains a perfluoroalkylene skeleton and two or more terminal radical polymerizable groups, and   (C) a photopolymerization initiator and/or a thermal polymerization initiator.       

     The present also provides an optical part, in particular, an optical waveguide, formed by photo-and/or thermo-curing the above curable resin composition.

TECHNICAL FIELD

The present invention relates to a curable resin composition, an opticalpart and an optical waveguide. More specifically, the present inventionrelates to a curable resin composition that forms a cured product thatis superior in heat resistance and has a precisely controlled refractiveindex through a photo-curing process and/or thermo-curing process, andalso concerns an optical part and an optical waveguide formed by such acured product.

BACKGROUND ART

Optical parts, formed by using polymer materials, include opticallenses, such as micro-lenses, micro-lens -arrays, Fresnel-lenses,lenticular-lenses, prism-sheets, diffraction gratings, non-sphericallenses, camera-lenses, glass lenses, and optical communication parts,such as optical fibers, optical waveguides and optical switches. In anyof these optical parts, it is important to control the refractive index,and among these, with respect to the optical waveguides, the refractiveindex should be precisely controlled to a level of the third digit ormore below the decimal point. Since the precise control of therefractive index is influenced not only by the polymer materials, butalso by forming methods of the optical waveguide, various polymermaterials for use in optical waveguides as well as many forming methodsfor optical waveguides have been proposed. The forming methods aremainly classified as follows.

Selective polymerization method: A polymer-film (substrate) isimpregnated with a monomer (the resulting polymer after aphoto-polymerization has a refractive index smaller than that of thesubstrate) containing a photo-polymerization initiator, and only theclad portion of the resulting film is then irradiated with light througha photo-mask to undergo a polymerizing reaction. Thereafter, the monomeron the un-irradiated portion (core portion) is removed by using asolvent or the like so that an optical waveguide is formed.

Photolithography +RIE method: After an optical waveguide layer has beenformed through photolithography, a core portion is formed thereinthrough dry-etching, and an upper clad portion is applied thereto andformed thereon.

Direct exposing method: After a core portion has been formed throughphotolithography, an upper clad portion is applied thereto and formedthereon.

Bleach method: Only the clad portion, which corresponds to a desiredportion of a polymer film, is irradiated with energy such as lightthrough a photo-mask to undergo a chemical reaction so that therefractive index is changed; thus, a waveguide is formed.

Stamper method: Onto a monomer (lower clad portion) applied to asubstrate, a recessed section is formed in a cured state by using astamper, and a monomer is then injected into the recessed section to becured to form a core portion, and an upper clad portion is formedthereon lastly.

Among these forming methods, it is considered that the stamper method ismost prospective from the viewpoints of productivity and low costs, anda radically polymerizable acrylate-monomer or a photo-cationicpolymerizable epoxy resin is suitable for this forming method.

For example, the use of a fluorinated epoxy resin or a fluorinatedepoxy(meth)acrylate-monomer has been proposed (Japanese PatentApplication Laid-Open No. 6-174956); however, since the hydroxide groupis contained in the cured polymer, the resulting problem is that a greatoptical loss is caused in the wavelength band for use in lightcommunication, in particular, in a band of 1550 nm. A straight-chainfluorine-containing (meth)acrylate-monomer, which contains noepoxy(meth)acrylate group, is also commercially available; however, thismonomer is poor in heat resistance, and in particular, during anassembling process using solder under a high temperature, the polymertends to be deformed and colored, and causes a problem of poor heatresistance, such as a thermal decomposition.

An active energy-ray curing-type composition for use in optical lenses,which is composed of a fluorine-containing compound, such as afluorine-containing (meth)acrylate-monomer, and its homopolymer or itscopolymer with another (meth)acrylate-monomer, and a non-fluorinepolyfunctional (meth)acrylate-monomer, has been proposed (JapanesePatent Application Laid-Open No. 2001-74912). With respect to thenon-fluorine polyfunctional (meth)acrylate-monomer, for example,aliphatic or aromatic polyvalent(meth)acrylates anddicyclopentenyl(meth)acrylate have been proposed. Although theseproposals have achieved a low refractive index of a cured product(optical lens), a problem arises in which a heat-resistant property islowered to cause a poor heat resistant decomposing property and acoloring-resistant property under a high temperature.

In order to solve the above-mentioned problems of the optical loss andinsufficient heat resistance, a method, which uses fluorinated polyimideas a main skeleton to ensure a sufficient heat resistance, has beenproposed (Japanese Patent Application Laid-Open No. 7-36068); however,an optical waveguide, made from a polymer which has a main skeletoncomposed of fluorinated polyimide, has the following problems:

(1) Insufficient moisture-resistant property,

(2) High birefringence due to an aromatic ring, and

(3) Difficulty in controlling refractive index.

As described above, in the conventional techniques, it has been verydifficult to achieve both of a heat-resistant property of a polymermaterial, such as a heat resistant decomposing property and acoloring-resistant property under a high temperature, and arefractive-index control to a level of the third digit or more below thedecimal point.

DISCLOSURE OF THE INVENTION

(Problems to be Solved by the Invention)

The present invention has been made to solve the above-mentionedconventional problems.

The objective of the present invention is to provide a curable resincomposition that is desirably used for manufacturing an optical partthat is superior in heat-resistant properties such as a heat-resistantdecomposing property and a coloring-resistant property, and has itsrefractive index precisely controlled, and, in particular, for formingan optical waveguide by using a stamper method.

In the present specification, the expression “has its refractive indexprecisely controlled” indicates that, with respect to a plurality ofcured products that have been repeatedly cured and formed from the samecurable resin composition, deviations in the refractive index thereofare controlled to a level of the fourth digit below the decimal point,more specifically, within a range of ±0.0005.

(Means to Solve the Problems)

In order to achieve the above-mentioned objectives, the inventors, etc.of the present invention have conducted extensive researches on thecombination of polymerizable monomers, and found that only when specifictwo kinds of polymerizable monomers are combined, the above-mentionedobjectives can be achieved; thus, the present invention has beendevised.

In other words, the present invention provides a curable resincomposition that contains the following components (A), (B) and (C) asessential components:

(A) a monomer that contains a polycyclic alicyclic hydrocarbon skeletonand two or more terminal radical polymerizable groups,

(B) a monomer that contains a perfluoroalkylene skeleton and two or moreterminal radical polymerizable groups, and

(C) a photopolymerization initiator and/or a thermal polymerizationinitiator.

The present invention also provides a cured product and an optical part,that is, in particular, an optical waveguide, which are formed byphoto-curing and/or thermo-curing the above-mentioned curable resincomposition.

(Effects Superior to Prior Arts)

The cured product formed by the curable resin composition of the presentinvention not only has a superior heat-resistance and a refractive indexthat is precisely controlled, but also exerts advantages such as a lowoptical loss and a superior stamper releasing property. Therefore, thecurable resin composition of the present invention serves as a polymermaterial that is desirably applied to various optical parts such asoptical lenses and optical communication parts, and is more particularlyapplied to a polymer material used for optical waveguides that require aprecise controlling process on the refractive index. The cured productof the present invention has such advantages that it can be used forapplications other than optical parts, such as heat-resistant coating,abrasion-resistant coating and water-repellant coating materials.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a flow chart of a sequence of processes that shows one exampleof a method for forming an optical waveguide by using a curable resincomposition of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

As described above, the curable resin composition of the presentinvention contains the following components (A), (B) and (C) asessential components:

(A) a monomer that contains a polycyclic alicyclic hydrocarbon skeletonand two or more terminal radical polymerizable groups (hereinafter,referred to as component (A)),

(B) a monomer that contains a perfluoroalkylene skeleton and two or moreterminal radical polymerizable groups (hereinafter, referred to ascomponent (B)), and

(C) a photopolymerization initiator and/or a thermal polymerizationinitiator (hereinafter, referred to as component (C)).

The following description will discuss embodiments of the presentinvention in detail.

“Component (A)”

A monomer, which serves as component (A) of the present invention,contains a polycyclic alicyclic hydrocarbon skeleton and two or moreterminal radical polymerizable groups. The alicyclic hydrocarbonskeleton means a cyclic hydrocarbon skeleton that does not exhibitaromatic properties. The alicyclic hydrocarbon skeletons includemono-cyclic and poly-cyclic, that is, di-cyclic or more, skeletons, andin the broader definition, also include terpenes and steroids. In thepresent invention, in order to allow the cured product to have asuperior heat-resistant property, a polycyclic alicyclic hydrocarbonskeleton of dicyclic or more, with a particularly bulky molecularstructure, needs to be used. More preferably, a polycyclic alicyclichydrocarbon skeleton of tricyclic or more is preferably used. Themonomer having a mono-cyclic alicyclic hydrocarbon skeleton causes aninsufficient heat-resistant property, failing to achieve the objectivesof the present invention. In the case of a monomer having an aliphatichydrocarbon skeleton that is a monomer having a hydrocarbon skeletonother than the alicyclic hydrocarbon skeleton, the resulting curedproduct has an insufficient heat-resistant property, and in the case ofa monomer having an aromatic hydrocarbon skeleton, as generally known,the birefringence of the cured product becomes greater due to thearomatic ring, and the heat-resistant property thereof is alsoinsufficient.

The polycyclic aliphatic hydrocarbon skeleton may have an innerunsaturated bond, such as a double or triple bond, and may also have asubstituent of a lower alkyl group the number of carbon atoms of whichis comparatively small. With respect to the number of carbon atomsinside each ring forming the polycyclic alicyclic hydrocarbon skeleton,the number of carbon atoms in a range of 3 to 12 has been known;however, the number of carbon atoms of 5 to 8, which is chemically morestable, is preferable, and a polycyclic alicyclic hydrocarbon skeletonconstituted by a ring with 5 to 6 carbon atoms is particularlypreferable.

Specific examples of the polycyclic alicyclic hydrocarbon skeletoninclude: bicyclic skeletons, such as bicyclo[2.1.1]hexane,bicyclo[4.1.0]heptane, bicyclo[2.2.1]heptane(norbornene),bicyclo[3.2.1]octane, bicyclo[4.2.0]octane, bicyclo[4.3.0] nonane,bicyclo[4.4.0]decane(decahydronaphthalene), and bicyclo[4.2.2]decane,tricyclic skeletons, such as tricyclo[5.2.1.0^(2,6)]decane,tricyclo[3.3.1.1^(3,7)]decane (adamantane) andtricyclo[6.2.1.0^(2,7)]undecane, and tetracyclic skeletons, such astetracyclo[6.2.1.1^(3,6)0.0^(2,7)]dodecane.

The terminal radical polymerizable group, possessed by the monomercorresponding to component (A) of the present invention, means aterminal unsaturated bonding group that is positioned at the terminal ofa monomer molecule, and is radically polymerizable by eitherphoto-irradiation or heating in the presence of a photopolymerizationinitiator or a thermal polymerization initiator (component (C)). Withrespect to the radical polymerizable group, specific examples thereofinclude: a (meth)acryloyloxy group, a (meth)acrylamide group, a vinylgroup (including an allyl group and a methallyl group, the same is truein the following description), an ethynyl group, an isopropenyl group, avinyl ether group, a vinyl thioether group, a vinyl ketone group, avinyl ester group and a vinyl amino group. In the present specification,the notations such as (meth)acryloyloxy group and (meth)acrylamide grouprespectively represent both of the acryloyloxy group and methacryloyloxygroup and both of the acrylamide group and methacrylamide group.

The monomer of component (A) needs to have two or more polymerizinggroups, which are selected from the group of the above-mentionedterminal radical polymerizable groups. In the case of the monomer thathas a polycyclic alicyclic hydrocarbon skeleton and only one terminalradical polymerizable group, even through an unsaturated bond isincluded in the skeleton, there is a big difference in polymerizingproperty between the terminal radical polymerizable group and theunsaturated bond of the skeleton; therefore, normally, only thepolymerizing reaction of the terminal radical polymerizable group isavailable, with the result that the cured product becomes insufficientin the heat-resistant property.

When selected from the viewpoints of curing property (polymerizingproperty) and physical properties of the cured product, a desirableterminal radical polymerizable group possessed by the monomer ofcomponent (A) includes a (meth)acryloyloxy group and a vinyl group, andthe monomer of component (A) of the present invention needs to have twoor more of these radical polymerizable groups. The two or more terminalradical polymerizable groups possessed by the monomer may be differentfrom each other or may be the same. A more preferably terminal radicalpolymerizable group is a (meth)acryloyloxy group, and a monomer having apolycyclic alicyclic hydrocarbon skeleton of tricyclic or more havingtwo or more (meth)acryloyloxy groups is most preferably used. Specificexamples of preferable monomers include: dimethyloltricyclo[5.2.1.0^(2,6)]decane di(meth)acrylate, 1,3-dimethyloltricyclo[3.3.1.1^(3,7))decane di(meth)acrylate,tricyclo[3.3.1.1^(3,7)]decane-1,3-diol di(meth)acrylate,1,3-bis(2-(meth)acryloyloxyethyloxycarbo) tricyclo[3.3.1.1^(3,7)]decaneand 1,3-bis(2-(meth)acryloyloxyethyloxycarbomethyl)tricyclo[3.3.1.1^(3,7)]decane.

With respect to the preparation method of the above-mentioned monomers,conventionally known methods, as they are, are used. For example,dimethylol tricyclo[5.2.1.0^(2,6)]decane and (meth)acrylic acid or(meth)acrylic acid chloride are allowed to undergo an esterificationreaction in a solvent to give dimethylol tricyclo(5.2.1.0^(2,6)]decanedi(meth)acrylate. For example,1,3-bis(carboxymethyl)tricyclo[3.3.1.1^(3,7)]decane and2-hydroxyethyl(meth)acrylate are allowed to undergo an esterificationreaction to prepare 1,3-bis(2-(meth)acryloyloxyethyloxycarbomethyl)tricyclo[3.3.1.1^(3,7)]decane.

“Component (B)”

A monomer, which serves as component (B) of the present invention, has aperfluoroalkylene skeleton and two or more terminal radicalpolymerizable groups. The perfluoroalkylene skeleton refers to askeleton structure in which all C—H bonds in an alkylene group aresubstituted by C—F bonds, and is generally referred to as aperfluoroalkylene group. The perfluoroalkylene group is generallyrepresented by general formula, —(CF₂)_(n)—. In this formula, n is aninteger in a range of 2 to 12, preferably in a range of 2 to 8. Theperfluoroalkylene group may have a lower perfluoroalkyl group as itsside chain group. The integer n exceeding 13 is not preferable, becausethis causes serious degradation in the heat-resistant property of thecured product.

In the case of a monomer having an alkylene group, a halogenatedalkylene group other than fluorine, or a fluorinated alkylene group inwhich one portion of the alkylene group is fluorinated, the resultingcured product has an insufficient heat-resistant property, failing toachieve the objective of the present invention.

The terminal radical polymerizable group possessed by the monomercorresponding to component (B) of the present invention is the same asthose exemplified as the monomer corresponding to component (A).

The monomer of component (B) needs to have two or more polymerizinggroups selected from the group of the above-mentioned terminal radicalpolymerizable groups. The monomer having only one terminal radicalpolymerizable group fails to provide a cured product having a superiorheat-resistant property. In the same manner as the monomer of component(A), when selected from the viewpoints of curing property and physicalproperties of the cured product, a desirable terminal radicalpolymerizable group possessed by the monomer of component (B) includes a(meth)acryloyloxy group and a vinyl group. The two or more terminalradical polymerizable groups possessed by the monomer may be differentfrom each other or may be the same. A more preferable terminal radicalpolymerizable group is a (meth)acryloyloxy group, and a monomer that hastwo or more terminal (meth)acryloyloxy groups and is composed of theaforementioned perfluoroalkylene group as its skeleton is particularlypreferable. Specific examples of preferable monomers include: a monomerthat directly has (meth)acryloyloxy methyl groups or 2-(meth)acryloyloxyethyl groups at the two terminals of a perfluoroalkylene group that isindicated by general formula, —(CF₂)_(m)— (m=2 to 12) and a monomer thatdirectly has 2-(meth)acryloyloxy ethyloxycarbo groups at the twoterminals of a perfluoroalkylene group that is indicated by generalformula, —(CF₂)_(n)— (n=2 to 8), and among the former monomer, C2–C8perfluoroalkylene-ω,ω′-bis ((meth)acryloyloxymethyl) andperfluoroalkylene-ω,ω′-bis (2-(meth)acryloyloxyethyl) are particularlypreferable monomers.

With respect to the preparation method of the above-mentioned monomers,conventionally known methods, as they are, are used. For example,perfluorotetramethylene-1,4-bis(hydroxymethyl) and (meth)acrylic acid or(meth)acrylic acid chloride are allowed to undergo an esterificationreaction in a solvent to prepareperfluorotetramethylene-1,4-bis((meth)acryloyloxymethyl). For example,perfluoro-tetramethylene-1,4-dicarboxylic acid and2-hydroxyethyl(meth)acrylate are allowed to undergo an esterificationreaction in a solvent to prepareperfluorotetramethylene-1,4-bis(2-(meth)acryloyloxyethyloxy carbo).

The compounding ratio between component (A) and component (B) of thecurable resin composition of the present invention is preferably set ina range of (A):(B)=80:20 to 55:45 (% by weight), preferably(A):(B)=75:25 to 60:40 (% by weight). In order to precisely control therefractive index of the cured product, it is more advantageous to makethe compounding rate of component (B) that has a lower refractive indexgreater; however, when the compounding rate thereof exceeds 45% byweight, the heat-resistant property of the cured product tends to belowered. In contrast, in the case when the compounding rate of component(B) is less than 20% by weight, although the heat-resistant property ofthe cured product is sufficient, it becomes difficult to preciselycontrol the refractive index.

“Component (C)”

A photo-polymerization initiator, which serves as component (C) of thepresent invention, is an essential component used for curing the curableresin composition of the present invention through photoirradiation.

With respect to the photo-polymerization initiator, not particularlylimited to a specific compound by the present invention, any of thefollowing generally-used photo-polymerization initiators may be used:carbonyl compound-based photo-polymerization initiators, such asacetophenones, benzophenones, diacetyls, benzyls, benzoins, benzoinethers, benzyldimethyl ketanols, benzoyl benzoates, hydroxyphenylketones and aminophenyl ketones; organic sulfur compound-basedphoto-polymerization initiators, such as thiuram sulfides andthioxanthones; and organic phosphor compound-based photo-polymerizationinitiators, such as acyl phosphine oxides and acyl phosphinic acidesters. In the present invention, each of these many kinds ofphoto-polymerization initiators may be used alone, or two or more kindsof these may be used in combination.

The compounding rate of photo-polymerization initiator (C) is set in arange of 0.5 to 10% by weight, preferably 1 to 7% by weight, withrespect to the total amount of component (A) and component (B). When thecompounding rate is less than 0.5% by weight, the photo-curing propertybecomes insufficient, and when the compounding rate exceeds 10%, thecuring reaction progresses too quickly and cause bad influences to thephysical properties of the cured product, failing to provide apreferable method.

With respect to the thermal polymerization initiator forming anothercomponent (C) of the present invention, among thermal polymerizationinitiators that are decomposed by heat to generate radicals, thosethermal polymerization initiators that have a thermal decomposingtemperature of about 30° C. or more, preferably about 60° C. or more,are used. With respect to those thermal polymerization initiators, amongcompounds generally used as thermal polymerization initiators for aradical polymerization reaction conventionally, organic peroxides thatproduce no by-products such as gases and water are more preferably used.The use of a thermal polymerization initiator having a thermaldecomposing temperature of about less than 30° C. makes the curableresin composition of the present invention instable.

Depending on chemical structures, organic peroxides are classified intoalkyl- or aryl-hydroperoxides, dialkyl- or diaryl-peroxides,alkyl-peroxide acids and esters thereof, diacyl-peroxides andketone-peroxides. In the present invention, any one of these organicperoxides may be used.

The compounding rate of the thermal polymerization initiator (C) ispreferably set in a range from 0.5 to 5% by weight, preferably from 1 to3% by weight, with respect to the total amount of component (A) andcomponent (B). The compounding rate of less than 0.5% by weight causesan insufficient thermo-curing property, and the compounding rateexceeding 5% by weight causes the curing reaction to progress tooabruptly and give adverse effects to the cured product. In the presentinvention, one kind of these organic peroxides may be used alone, or twokinds or more of these may be used in combination.

In the present invention, the photo-polymerization initiator and theorganic peroxide forming the thermal polymerization initiator arerespectively blended independently, or blended in combination. Uponblending in combination, the respective compounding rates are also setas described above.

With respect to the curable resin composition of the present invention,a monomer other than the above-mentioned component (A) and component (B)of the present invention, which has one or more terminal radicalpolymerizable groups attached to a terminal of the monomer molecule maybe blended thereto as a reactive diluent. The reactive diluent isblended when adjustments in the viscosity or curing property of thecurable resin composition of the present invention or in the physicalproperties of the cured product are required. With respect to suchmonomers, a monomer, which has a (meth)acryloyloxy group or a vinylgroup that is the same terminal radical polymerizable group, ispreferably used, and a monomer, which has a (meth)acryloyloxy group, ismore preferably used, so as to allow component (A) and component (B) tohave the same photo-curing property and thermo-curing property. Amonomer having two or more (meth)acryloyloxy groups is more preferablyused. Specific examples thereof include a polyvalent(meth)acrylate-monomer of divalent or more, such as an aliphatic groupmonomer and a single-ring alicyclic group monomer.

The compounding rate of the reactive diluent is preferably set to 20% byweight or less with respect to the total amount of component (A) andcomponent (B). The compounding rate exceeding 20% by weight is notpreferable since it causes serious degradation in the heat resistantproperty of the cured product.

To the curable resin composition of the present invention, a smallamount of additives, such as a polymerization inhibitor, an antifoam, aphoto-stabilizer, a thermal stabilizer, a leveling agent, a couplingagent and an antistatic agent, may be added, if necessary, as long asthe addition is limited to a range so as not to interfere with thephoto-curing or thermo-curing reaction.

In the case of the photo-curing reaction with photo-polymerizationinitiator (C) added thereto, irradiation with ultraviolet rays isgenerally carried out. With respect to the light source of ultravioletrays, examples thereof include: a super-high pressure mercury lamp, ahigh pressure mercury lamp, a low pressure mercury lamp, a metal halidelamp, a carbon arc light and a xenon lamp, and a high pressure mercurylamp or a metal halide lamp is preferably used. Although differentdepending on the component composition of the curable resin composition,the dose of ultraviolet-ray irradiation is normally set in a range from1000 to 5000 mJ/cm².

In the case of the thermo-curing reaction with an organic peroxideserving as the thermal polymerization initiator (C) added thereto, thecuring process is carried. out by heating the resin composition to atemperature above the thermal-decomposing temperature of the organicperoxide. Therefore, although depending on the kinds of the organicperoxide to be added, the heating temperature is normally set in a rangefrom 10 to 60 minutes.

In the case of a curing process which is a combination of thephoto-curing and thermo-curing processes with both of thephoto-polymerization initiator and the organic peroxide added thereto,in general, after the photo-curing process has been carried out throughirradiation with ultraviolet-rays, the thermo-curing process is carriedout by a heating operation to complete the curing process. In comparisonwith the thermo-curing process, the photo-curing process is superior inhandling, curing speed and the like; therefore, in the curable resincomposition of the present invention, the photo-curing process, that is,the curing process using ultraviolet-rays, is preferably used.

The cured product to be formed by photo-curing and/or thermo-curing thecurable resin composition of the present invention is superior inheat-resistant properties, such as a heat-resistant decomposing propertyand a coloring-resistant property, and has its refractive indexprecisely controlled. Therefore, the curable resin composition of thepresent invention is preferably used for forming the aforementionedoptical parts. In the case when an optical waveguide is formed by usingthe curable resin composition of the present invention through aphoto-curing stamper method, the forming property of the stamper methodis very good, and the resulting optical waveguide also has the advantageof a reduced optical loss; therefore, the curable resin composition isin particular suitable for the formation of an optical waveguide.

Referring to FIG. 1, the following description will discuss a method forforming an optical waveguide by using the curable resin composition ofthe present invention. The method shown in FIG. 1 corresponds to thestamper method; however, the optical waveguide of the present inventionmay be formed by using a conventionally known method, such as theaforementioned photolithography +RIE method and direct exposing method.The curable resin composition of the present invention may be used forforming only either one of a clad portion 2 (lower portion 2 a; upperportion 2 b) and a core portion 3 of the optical waveguide 1 (see FIG.1(F)); however, it is preferably used for forming both of the members.The optical waveguide is formed so that the refractive index of the cladportion is made slightly lower than the refractive index of the coreportion. In the case when both of the clad portion and the core portionare made from the curable resin composition of the present invention,the adjustments of the refractive indexes of the clad portion and thecore portion can be made by slightly changing the compounding ratio ofmonomer component (A) and monomer component (B).

Upon forming the optical waveguide, as shown in FIG. 1(A), first, acurable resin composition 12 a for a lower clad portion is applied to asubstrate 10 through a known method such as a spin-coat method and adoctor blade method, and a convex-type stamper 11 is pressed thereon. Inthis pressed state, a photo-curing process or/and a thermo-curingprocess is carried out so that a lower clad portion 2 a having anengraved section 13 corresponding to a core portion is formed (FIGS.1(B) and 1(C)). After the convex-type stamper has been released, theengraved section 13 is filled with a curable resin composition 14 forthe core portion, and a photo-curing process or/and a thermo-curingprocess is carried out with a flat plate 15 pressed thereon to form acore portion 3 (FIG. 1(D)). Lastly, a curable resin composition 12 b foran upper clad portion is applied thereto, and a photo-curing processor/and a thermo-curing process is carried out with a substrate 16pressed thereon to form an upper clad portion 2 b (FIG. 1(E)); thus, thesubstrate is removed so that an optical waveguide 1 is completed (FIG.1(F)). Here, with respect to the substrates 10 and 16, transparentsubstrates such as glass plates are used when the photo-curing processis carried out.

EXAMPLES

The following description will discuss the present invention in detailby means of examples; however, the present invention is not intended tobe limited by the examples.

The heat-resistant property and the precise-controlling property for therefractive index were measured by using the following testing methods.

Heat-Resistance Test

A curable resin composition was injected between two glass plates(thickness: 0.7 mm, size: 10 cm×10 cm) that were held with a gap of 20±1μm, with spacer tapes inserted in between, and this was then irradiatedwith ultraviolet rays by using a high-pressure mercury lamp until thedose of ultraviolet-ray irradiation on the glass surface reached 3,000mJ/cm².

The glass plates were separated so that a resin film that had beenphoto-cured was taken out, and measuring-use test pieces (weight=10 mg)were sampled from the center portion thereof. Successively, the testpieces were heated at a temperature-raising rate of 10° C./min from roomtemperature to 250° C. by using a TG-DTA measuring device (model: 220,made by Seiko Instruments Inc.) so that upon reaching 250° C., theweight loss rate due to heat was measured to obtain the results ofmeasurements on the heat-resistant property. The degree of coloring ofthe test pieces after the measurements was visually determined.

Tests for Precise-Controlling Property of the Refractive Index

The same sequence of processes under the same conditions as those of themanufacturing processes for the test pieces used for heat-resistantmeasurements were carried out five times independently so thatphoto-cured resin films were formed from the same curable resincomposition, and by measuring the refractive indexes in the centerportions of the respective cured resin films, deviations in therefractive indexes were calculated. The measurements of the refractiveindexes were carried out through a prism coupling method by using aprism coupler (model 2010, made by Metricon Corporation) to significantfigures of 4 digits under the decimal point at 23° C.

Example 1

Dimethylol tricyclo[5.2.1.0^(2,6)]decane diacrylate (Tradename: LightAcrylate DCP-A, made by Kyoeisha Chemical Co., Ltd.)(7.000 g),perfluoro-octamethylene-1,8-bis(acryloyloxymethyl) (Tradename:Fluorolite FA-16, made by Kyoeisha Chemical Co., Ltd.)(3.000 g) andDarocure 1173 serving as a photo-polymerization initiator (made by CibaSpecialty Chemicals Corp.)(0.200 g) were mixed and dissolved to preparea curable resin composition (I) of the present invention.

By using this curable resin composition (I), a photo-cured resin filmwas obtained through the above-mentioned method. The transparency of theresulting photo-cured resin film was excellent. The weight loss rate dueto heat measured by the heat-resistance test conducted on thephoto-cured resin film was less than 1%, ensuring a superiorheat-resistant property. No coloring was found on the test pieces afterthe heat-resistance test. The deviations in refractive indexes werewithin a range of 1.4923±0.0003 so that a superior precise-controllingproperty of the refractive index was obtained.

Comparative Example 1

The same components of the same amounts as Example 1 were blended exceptthat in place of dimethylol tricyclo[5.2.1.0^(2,6)]decane diacrylate ofExample 1, tricyclo[5.2.1.0^(2,6)]-3-decenyl acrylate (Tradename:FA-511A, made by Hitachi Chemical Co., Ltd.) (7.000 g) was used so thata curable resin composition (1) was prepared.

The same processes were carried out by using this curable resincomposition (1) to obtain a photo-cured resin film. This photo-curedresin film was white and cloudy, and the rate of weight decrease due tothe heat-resistance test was 30%, which was extremely high, and the testpieces were colored into yellow.

Comparative Example 2

The same components of the same amounts as Example 1 were blended exceptthat in place of dimethylol tricyclo[5.2.1.0^(2,6)]decane diacrylate ofExample 1, bisphenol A diglycidyl ether-methacrylic acid 2-mol adduct(Tradename: Epoxyester 3000A, made by Kyoeisha Chemical Co., Ltd.)(7.000 g) was used so that a curable resin composition (2) was prepared.

The same processes were carried out by using this curable resincomposition (2) to obtain a photo-cured resin film. This photo-curedresin film was white and cloudy, and the rate of weight decrease due tothe heat-resistance test was 10%, which was very high, and the testpieces were colored into yellow.

Comparative Example 3

The same components of the same amounts as Example 1 were blended exceptthat in place of dimethylol tricyclo [5.2.1.0^(2,6)]decane diacrylate ofExample 1, neopentyl glycol diacrylate (7.000 g) was used so that acurable resin composition (3) was prepared.

The same processes were carried out by using this curable resincomposition (3) to obtain a photo-cured resin film. This photo-curedresin film was white and cloudy, and the rate of weight decrease due tothe heat-resistance test was 21%, which was very high, and the testpieces were colored into yellow.

Comparative Example 4

The same components of the same amounts as Example 1 were blended exceptthat in place of dimethylol tricyclo[5.2.1.0^(2,6)]decane diacrylate ofExample 1, 1,4-dimethylolcyclohexane diacrylate (7.000 g) was used sothat a curable resin composition (4) was prepared.

The same processes were carried out by using this curable resincomposition (4) to obtain a photo-cured resin film. This photo-curedresin film was slightly cloudy, and the rate of weight decrease due tothe heat-resistance test was 13%, which was very high, and the testpieces were considerably colored into yellow.

Comparative Example 5

The same components of the same amounts as Example 1 were blended exceptthat in place of perfluoro-octamethylene-1,8-bis(acryloyloxymethyl) ofExample 1, perfluorooctylethyl acrylate (Tradename: Light AcrylateFA-108, made by Kyoeisha Chemical Co., Ltd.)(3.000 g) was used so that acurable resin composition (5) was prepared.

The same processes were carried out by using this curable resincomposition (5) to obtain a photo-cured resin film. This photo-curedresin film was white and cloudy, and the rate of weight decrease due tothe heat-resistance test was 15%, which was very high, and the testpieces were slightly colored into yellow.

Example 2

By using a normally-used method in which1,3-bis(carboxymethyl)tricyclo[3.3.1.1^(3,7)]decane (1,3-adamantanediacetic acid) (made by Tokyo Kasei Kogyo Co., Ltd.) and excessive2-hydroxyethyl acrylate (Tradename: Light Ester HOA, made by KyoeishaChemical Co., Ltd.) were added to a toluene solvent and allowed toundergo an esterification reaction therein, and 2-hydroxyethyl acrylatethat had not been reacted with the solvent was then distilled off,solid-state 1,3-bis(2-acryloyloxyethyloxycarbomethyl)tricyclo[3.3.1.1^(3,7)]decane was obtained.

The resulting 1,3-bis(2-acryloyloxyethyloxycarbomethyl)tricyclo[3.3.1.1^(3,7)]decane (6.000 g),perfluorotetramethylene-1,4-bis(acryloyloxymethyl) (Tradename: F06086D,made by AZmax Co., Ltd.)(3.500 g), 1,4-dimethylol cyclohexane diacrylate(0.500 g) and t-butylperoxy acetate (0.200 g) were mixed and dissolvedto prepare a curable resin composition (II) of the present invention.

In the same manner as the preparation process of the test piece of theaforementioned heat-resistance test method, after this curable resincomposition (II) had been injected into a gap between two glass plates,the resulting sample was placed in a heating furnace, and heated at 100°C. for 40 minutes, and successively heated at 120° C. for 10 minutes sothat a thermo-cured resin film was obtained. This thermo-cured resinfilm was excellent in transparency. The weight loss rate due to heatafter the heat resistance test was 1% or less, which indicated asuperior heat resistance. No coloring was found on the test pieces afterthe heat-resistance test. The deviation in refractive indexes was withina range of 1.5015±0.0003 so that a superior precise-controlled propertyof the refractive index was obtained.

Comparative Example 6

By using a normally-used method in which 1-carboxymethyltricyclo[3.3.1.1^(3,7)]decane (1-adamantane acetic acid) (made by TokyoKasei Kogyo Co., Ltd.) and excessive 2-hydroxyethyl acrylate (the sameas described above) were added to a toluene solvent and allowed toundergo an esterification reaction therein, and 2-hydroxyethyl acrylatethat had not been reacted with the solvent was then distilled off,solid-state 1-(2-acryloyloxyethyloxycarbomethyl)tricyclo[3.3.1.1^(3,7)]decane was obtained.

The same components with same amounts as those of Example 2 were blendedexcept that 6.000 g of the resulting 1-(2-acryloyloxyethyloxycarbomethyl)tricyclo[3.3.1.1^(3,7)]decane was used in place of1,3-bis(2-acryloyloxyethyloxy carbomethyl)tricyclo[3.3.1.1^(3,7)]decaneused in Example 2 so that a curable resin composition (6) was prepared.

By using this curable resin composition (6), the same processes as thoseof Example 2 were carried out so that a thermo-cured resin film wasobtained. This thermo-cured resin film was white and cloudy, and therate of weight decrease due to the heat-resistance test was 10%, whichwas a very high level, with the result that the test pieces were coloredinto yellow.

Comparative Example 7

The same components with same amounts as those of Example 2 were blendedexcept that 3.500 g of 2-(perfluorobutyl)ethyl acrylate (Tradename:F05906D-D, made by AZmax Co., Ltd.) was used in place ofperfluorotetramethylene-1,4-bis(acryloyloxymethyl) so that a curableresin composition (7) was prepared.

By using this curable resin composition (7), the same processes as thoseof Example 2 were carried out so that a thermo-cured resin film wasobtained. This thermo-cured resin film was white and cloudy, and therate of weight decrease due to the heat-resistance test was 20%, whichwas a very high level, with the result that the test pieces wereslightly colored into yellow.

Example 3

With respect to the optical waveguide, it is necessary to provide adifference in refractive indexes of about 0.50% between a core portionand a clad portion. The curable resin composition (I) relating toExample 1 was used as the core portion, and a curable resin composition(III), formed by mixing and dissolving 7.000 g of dimethyloltricyclo[5.2.1.0^(2,6)]decane diacrylate (the same as describedearlier), 3.300 g of perfluoro-octamethylene-1,8-bis(acryloyloxymethyl)(the same as described earlier) and 0.206 g of Darocure 1173 (the sameas described earlier), was used as the clad portion so that an opticalwaveguide was formed by using the following method.

After the curable resin composition (III) had been applied to a glasssubstrate, this was photo-cured (dose of ultraviolet-rayirradiation=3,000 mJ/cm²) with a convex-type stamper (metal mold:convex-type dimension=5 μm×5 μm×10 mm) being pressed thereon, and theconvex-type stamper was released so that a lower clad portion having anengraved portion corresponding to the core portion was formed.

The curable resin composition (I) was injected into the engravedportion, and this was photo-cured (dose of ultraviolet-rayirradiation=3,000 mJ/cm²) with a flat plate being pressed thereon sothat a core portion was formed. Each of the stampers had a goodreleasing property.

The curable resin composition (III) was applied thereto, and this wasphoto-cured (dose of ultraviolet-ray irradiation=3,000 mJ/cm²) with aglass substrate being pressed thereon so that an upper clad portion wasformed.

The core portion of the optical waveguide thus formed was cut by thesection, and the state of the section was observed after a heatresistance test of 250° C.×5 minutes; however, no change was observed onthe appearance. Optical waveguide was confirmed. The measured values ofoptical loss were 0.4 dB/cm at 1,310 nm and 0.9 dB/cm at 1,550 nm, whichwere superior values.

Comparative Example 8

A curable resin composition (8), formed by mixing and dissolving 8.000 gof dimethylol tricyclo[5.2.1.0^(2,6)]decane diacrylate (the same asdescribed earlier), 2.000 g of octamethylene glycol 1,8-diacrylate and0.200 g of Darocure 1173 (the same as described earlier), was used asthe core portion, and a curable resin composition (9), formed by mixingand dissolving 3.000 g of dimethylol tricyclo[5.2.1.0^(2,6)]decanediacrylate (the same as described above), 7000 g of triethylene glycoldiacrylate and 0.200 g of Darocure 1173 (the same as described above),was used as the clad portion so that an optical waveguide was formed byusing the same processes as those of Example 3.

The core portion of the optical waveguide thus formed was cut by thesection, and the state of the section was observed after a heatresistance test of 250° C.×5 minutes, with the result that distortionand boundary separation from the clad portion occurred in the coreportion. No optical waveguide was confirmed.

1. A curable resin composition, comprising: a monomer that contains apolycyclic alicyclic hydrocarbon skeleton and two or more terminalradical polymerizable groups, a monomer that contains aperfluoroalkylene skeleton and two or more terminal radicalpolymerizable groups, and a photopolymerization initiator and/or athermal polymerization initiator.
 2. The curable resin compositionaccording to claim 1, wherein the terminal radical polymerizable groupsare (meth)acryloyloxy groups.
 3. The curable resin composition accordingto claim 2, wherein the polycyclic alicyclic hydrocarbon skeleton is atricyclic or more skeleton.
 4. The curable resin composition accordingto claim 2, wherein the perfluoroalkylene skeleton is aperfluoroalkylene skeleton having carbon atoms of 2 to
 8. 5. The curableresin composition according to claim 2, wherein the monomer thatcontains a perfluoroalkylene skeleton and two or more terminal radicalpolymerizable groups isperfluoroalkylene-ω,ω′-bis((meth)acryloyloxymethyl) or-bis(2-(meth)acryloyloxyethyl) having carbon atoms of 2 to
 8. 6. A curedproduct, formed by photo-curing and/or thermo-curing the curable resincomposition according to claim 2, and showing both of a superior heatresistant property and a refractive index that is precisely controlled.7. The curable resin composition according to claim 1, wherein thepolycyclic alicyclic hydrocarbon skeleton is a tricyclic or moreskeleton.
 8. The curable resin composition according to claim 7, whereinthe perfluoroalkylene skeleton is a perfluoroalkylene skeleton havingcarbon atoms of 2 to
 8. 9. The curable resin composition according toclaim 7, wherein the monomer that contains a perfluoroalkylene skeletonand two or more terminal radical polymerizable groups isperfluoroalkylene-ω,ω′-bis((meth)acryloyloxymethyl) or-bis(2-(meth)acryloyloxyethyl) having carbon atoms of 2 to
 8. 10. Acured product, formed by photo-curing and/or thermo-curing the curableresin composition according to claim 7, and showing both of a superiorheat resistant property and a refractive index that is preciselycontrolled.
 11. The curable resin composition according to claim 1,wherein the perfluoroalkylene skeleton is a perfluoroalkylene skeletonhaving carbon atoms of 2 to
 8. 12. The curable resin compositionaccording to claim 11, wherein the monomer that contains aperfluoroalkylene skeleton and two or more terminal radicalpolymerizable groups isperfluoroalkylene-ω,ω′-bis((meth)acryloyloxymethyl) or-bis(2-(meth)acryloyloxyethyl) having carbon atoms of 2 to
 8. 13. Acured product, formed by photo-curing and/or thermo-curing the curableresin composition according to claim 11, and showing both of a superiorheat resistant property and a refractive index that is preciselycontrolled.
 14. The curable resin composition according to claim 1,wherein the monomer that contains a perfluoroalkylene skeleton and twoor more terminal radical polymerizable groups isperfluoroalkylene-ω,ω′-bis((meth)acryloyloxymethyl) or-bis(2-(meth)acryloyloxyethyl) having carbon atoms of 2 to
 8. 15. Acured product, formed by photo-curing and/or thermo-curing the curableresin composition according to claim 14, and showing both of a superiorheat resistant property and a refractive index that is preciselycontrolled.
 16. A cured product, formed by photo-curing and/orthermo-curing the curable resin composition according to claim 1, andshowing both of a superior heat resistant property and a refractiveindex that is precisely controlled.
 17. An optical part made of thecured product according to claim
 16. 18. An optical waveguide made ofthe cured product according to claim 17.